Biosensors are devices for sensing and detecting biomolecules and operate on the basis of electronic, electrochemical, optical, and/or mechanical detection principles. Biosensors can sense charges, photons, and mechanical properties of bio-entities or biomolecules, or through molecular tags. The detection can be performed by detecting the bio-entities or biomolecules themselves, or through interaction and reaction between specified reactants and bio-entities/biomolecules. Biosensors continue to be miniaturized to reduce sample size while increasing sensitivity and information content.
A flow cell is a type of biosensor that includes micro-fluidic structures that allows external detection of its contents through a transparent window, for example, with microscopes, spectroscopes, or refractometers. The flow cell includes many capture sites on which biochemical reactions occur. The capture sites may be patterned or unpatterned (randomly distributed) on or in one or several microfluidic channels. Flow cells may be used to analyze biomolecules, conduct reactions, and irradiate samples. For example, flow cells may be used to for deoxyribonucleic acid (DNA) sequencing using fluorescent dyes for optical sensing.
Optical sensing techniques continue to improve, primarily from using better cameras with more pixels and better sensitivity to obtain more information from a flow cell. To benefit from the improved optical sensing techniques, the capture sites in flow cells are further miniaturized using semiconductor processing techniques. Challenges in fabrication of the flow cells using semiconductor processes arise, for example, due to compatibility issues between the semiconductor fabrication processes, the biological applications, and restrictions and/or limits on the semiconductor fabrication processes.